The present invention relates to transceivers in radio products. More specifically, the present invention relates to an apparatus for and method of improving efficiency in battery-operated portable transceivers.
Portable battery-powered radio products, such as cellular phones, are becoming increasingly compact as a result of the development of smaller and longer-lasting batteries. These batteries, however, typically do not have high output voltages. For instance, lithium batteries, commonly used in many cellular phone products, have an output voltage around 3.6 volts per cell. Such an output voltage, while useful in many applications, may not be sufficient for power amplifiers which typically require a higher supply voltage for optimum performance. Furthermore, different components within the portable radio products may require different power supply voltages for optimal performance. Thus, a voltage converter is often used to transform the battery voltage to other voltages as required by the specific applications.
One major drawback of using a voltage converter in portable radio products, however, is power dissipation. The problem is exacerbated in portable or mobile radio products where battery capacity is limited. Thus, even a lower level of dissipation by the voltage converter causes a significant decrease in battery life. In order to decrease power dissipation, switching voltage regulators are typically used as voltage converters. A switching voltage regulator is well known in the art and generally comprises a pass transistor which oscillates between cutoff and saturation. Thus, the pass transistor acts as a switch that is rapidly being turned on and off. The rapid switching, coupled with a network of inductors and capacitors, boosts up or bucks down an input voltage. A text-book example of such a switching voltage regulator can be found in Greenfield, J., Practical Transistors And Linear Integrated Circuits, pp. 505-515, John Wiley and Sons, Inc., 1988.
In order to further minimize power dissipation, highly complicated voltage regulators using state of the art components and designs have been devised. However, the level of dissipation remains relatively high. Indeed, in prior art battery-operated portable transceivers, the maximum overall transmitter power efficiency is limited to roughly 40% when the transmitter transmits at its maximum output power. A significant amount of energy is consumed by the switching voltage regulator. When the transmitter transmits at lower power levels, the overall transmitter power efficiency becomes even lower. Thus, what is needed is an apparatus for and method of increasing the efficiency of the voltage converters such that a minimum amount of energy is dissipated in the voltage converters. What is further needed is an apparatus for and method of adaptively controlling power supplied to power amplifiers and signal transmitters in battery-operated transceivers to achieve maximum efficiency.
Accordingly, the present invention provides a system for and method of minimizing power dissipation of voltage converters in radio products. The present invention also provides a mechanism for providing the minimum necessary power to the transceiver by adaptively providing a high power supply voltage and a low power supply voltage to the transceiver. Further, the present invention provides a mechanism and method for controlling a switching voltage regulator to supply a low power supply voltage at maximum efficiency. These and other advantages of the present invention not specifically mentioned above will become clear within discussions of the present invention presented herewith.
A system and method are described herein for minimizing power dissipation and power supplied to a transmitter or a power amplifier in a battery-operated mobile unit by adaptively controlling a voltage converter to provide a variable power supply voltage to the transmitter or power amplifier. In the preferred embodiment, the voltage converter is coupled to receive a source voltage from a battery, and is coupled to provide operating power to the transmitter or power amplifier. The voltage converter is also coupled to receive a control signal from a controller, which adaptively activates the voltage converter to transform the source voltage to a converted voltage, or deactivates the voltage converter to directly apply the source voltage to the power amplifier. Power dissipation is therefore minimized when conversion functions of the voltage converter are deactivated when voltage conversion is unnecessary.
In order to adaptively activate and deactivate conversion functions of the voltage converter, an appropriate supply voltage required for each possible transmitter output level is pre-determined. Then, during the operation of the transmitter and according to the required transmitter output level, an appropriate supply voltage to the transmitter is determined and compared to the source voltage. If the appropriate supply voltage is substantially equivalent to the source voltage, voltage conversion functions of the voltage converter are deactivated. As a result, the source voltage will be applied directly to the transmitter without significant dissipation. Whereas, if the appropriate supply voltage is higher than the source voltage, voltage conversion functions of the voltage converted are activated, causing the source voltage to be transformed to an up-converted voltage, which is then applied to the transmitter.
In furtherance of the preferred embodiment of the present invention, the voltage converter may include a switching voltage regulator for transforming the source voltage to an up-converted voltage. The controller may comprise a digital signal processor (DSP), microcontroller, or other types of microprocessor for providing an oscillating pulse to control the operation of the voltage regulator. A transmitter-amplifier is coupled to an output of the voltage regulator for receiving a power supply voltage. In the preferred embodiment, the power supply voltage is chosen to achieve maximum efficiency for a given signal power to be put out of the transmitter-amplifier.
In an alternate embodiment of the present invention, the mobile unit may include a battery having a high source voltage, a voltage regulator for down-converting the source voltage, and a signal transmitter or power amplifier coupled to receive the source voltage or a down-converted voltage from the voltage regulator. The mobile unit may also utilize a controller for providing an oscillating pulse to control the operation of the voltage regulator. When a high transmitter output level is necessary to transmit signals from the mobile unit to a base station, the controller deactivates the voltage conversion functions of the voltage regulator in order to directly apply the source voltage to the signal transmitter or the power amplifier.